Method and apparatus for transmitting CSI-RS and data using partial muting of CSI-RS

ABSTRACT

A method and apparatus for transmitting Channel State Information Reference Symbol (CSI-RS) and data with partial muting of the CSI-RS are proposed. The method includes determining a CSI-RS pattern to be used among CSI-RS pattern candidates, determining a muting pattern for muting some resource elements constituting CSI-RS pattern candidates except for the determined CSI-RS pattern, mapping data symbols and CSI-RS to resource elements in a resource grid with rate patching in consideration of the CSI-RS pattern and muting pattern, and transmitting the data symbols and CSI-RS to a terminal.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of a prior applicationSer. No. 13/156,685, filed on Jun. 9, 2011, which claimed the benefitunder 35 U.S.C. §119(a) of a Korean patent application filed on Jun. 11,2010 in the Korean Intellectual Property Office and assigned Serial No.10-2010-0055607, the entire disclosure of which is hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for transmittinga Channel State Information Reference Symbol (CSI-RS) and data. Moreparticularly, the present invention relates to a method and apparatusfor transmitting the CSI-RS and data with partial muting of the CSI-RS.

2. Description of the Related Art

Mobile communication systems are currently evolving from basiccommunication devices into high-speed, high-quality wireless packet datacommunication systems that provide data services and multimedia servicesbeyond the early voice-oriented services. Recently, various mobilecommunication standards, such as High Speed Downlink Packet Access(HSDPA) and High Speed Uplink Packet Access (HSUPA), both defined by3^(rd) Generation Partnership Project (3GPP), High Rate Packet Data(HRPD) defined by 3^(rd) Generation Partnership Project-2 (3GPP2), andInstitute of Electrical and Electronics Engineers (IEEE) 802.16, havebeen developed to support the high-speed, high-quality wireless packetdata services.

The 3^(rd) generation wireless packet data communication system of therelated art, such as HSDPA, HSUPA and HRPD, uses such technologies as anAdaptive Modulation and Coding (AMC) method and a channel-sensitivescheduling method in order to improve transmission efficiency. With theuse of the AMC method, a transmitter can adjust the amount oftransmission data according to the channel state. For example, when thechannel state is not good, the transmitter reduces the amount oftransmission data to match a reception error probability to a desiredlevel, and when the channel state is good, the transmitter increases theamount of transmission data to efficiently transmit a large volume ofinformation while matching the reception error probability to thedesired level. Using the channel-sensitive scheduling resourcemanagement method, the transmitter, since it selectively services a userhaving a superior channel state among several users, can increase in thesystem capacity, as compared with a transmitter that allocates a channelto one user and services the user with the allocated channel. Suchcapacity increase is commonly referred to as a multi-user diversitygain. In brief, the AMC method and the channel-sensitive schedulingmethod are methods for receiving partial channel state information beingfed back from a receiver, and applying an appropriate modulation andcoding technique at the most efficient time determined depending on thereceived partial channel state information.

Recently, intensive research is being conducted to replace Code DivisionMultiple Access (CDMA), which is the multiple access scheme used the2^(nd) and 3^(rd) generation mobile communication systems, withOrthogonal Frequency Division Multiple Access (OFDMA) in the nextgeneration mobile communication system. 3GPP and 3GPP2 have startedstandardization work on evolved systems based on OFDMA.

It is known that OFDMA, compared to CDMA, is expected to increasecapacity at least in part due to performing scheduling in the frequencydomain (i.e., Frequency Domain Scheduling). While capacity gain can beobtained from the time-varying channel characteristic using thechannel-sensitive scheduling method, more capacity gain can be obtainedusing the frequency-varying channel characteristic.

In order to increase the capacity gain with the aforementioned methods,the information on the status of the radio channel should be acquired.The more accurate the channel status information, the more the capacitygain can increase. In a case of the channel status informationmeasurement using a reference signal, the measurement accuracy isimproved as the signal to interference plus noise power ratio of thereceived reference signal is increased. Accordingly, the interferencepower to the received reference signal should be reduced in order toimprove to the channel status information accuracy. Among variousrelated art methods to reduce the interference to the reference signal,the present disclosure deals with a method to reduce the interference toreference signals transmitted by different transmitters using a mutingtechnique for keeping the time, frequency, antenna, and code resourcewith which the reference signal of another transmitter is transmittedempty.

FIG. 1 is a diagram illustrating a Channel State Information ReferenceSymbol (CSI-RS) reuse pattern and muting pattern according to therelated art.

Referring to FIG. 1, part (a) shows an exemplary CSI-RS pattern of whicha reuse factor is 6 for use in a Long Term Evolution Advanced (LTE-A)system.

In part (a) of FIG. 1, the Resource Elements (REs) numbered from 0 to 7and having the same background pattern shows a CSI-RS pattern per cell,and 6 different CSI-RS patterns are shown. For one cell, one CSI-RSpattern is used such that 6 adjacent cells can use different CSI-RSpatterns.

Part (b) of FIG. 1 shows an exemplary subframe in which a transmitter ofone cell transmits the CSI-RS. In a case of part (b) of FIG. 1, the celluses the CSI-RS pattern 0. Since the positions of the CSI-RS of othercells are used for data transmission, the signal of the cell can affectinterference to the CSI-RSs of the 5 adjacent cells using differentCSI-RS patterns. Likewise, the 5 adjacent cells affect interference tothe CSI-RS of the cell using the pattern of part (b) of FIG. 1. Suchinterferences degrade channel estimation performance based on theCSI-RS.

Part (c) of FIG. 1 shows an exemplary subframe using the mutingtechnique in which no data is transmitted on the resources that are usedfor CSI-RS transmission of other cells to mitigate channel estimationperformance degradation caused by interference. Since the subframeconfiguration of part (c) of FIG. 1 can reduce the interference toCSI-RS as compared to the subframe configuration of part (b) of FIG. 1,it is expected to improve the channel estimation performance based onthe CSI-RS. However, the subframe configuration of part (c) of FIG. 1uses a small number of REs for data transmission as compared to thesubframe configuration of part (b) of FIG. 1. Accordingly, in order tomaintain the same target error rate in both the cases of parts (b) and(c), the subframe of part (c) of FIG. 1 should be configured to transmitthe signal at a low Modulation and Coding Scheme (MCS) level as comparedto that in the subframe of part (b) of FIG. 1. In a case of part (c) ofFIG. 1, since the loss caused by the small number of REs fortransmitting data is more affective that the gain obtained by theimprovement of the channel estimation performance especially when alarge number of transmit antennas are used, the system throughputdecreases.

There is therefore a need to develop a novel muting technique differentfrom the related art method for addressing the system throughputdegradation caused by the shortage of REs for data transmission withoutcompromising the performance improvement effect caused by the channelestimation performance enhancement with the muting technique, and methodand apparatus for transmitting a control signal for supporting the novelmuting technique.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentinvention is to provide a method and apparatus for transmitting aChannel State Information Reference Signal (CSI-RS) and data that iscapable of increasing system throughput by improving channel estimationperformance, thereby addressing the system throughput degradationproblem caused by using the muting technique of the related art.

In accordance with an aspect of the present invention, a method fortransmitting, by a base station, CSI-RS and data is provided. The methodincludes determining a CSI-RS pattern to be used among CSI-RS patterncandidates, determining a muting pattern for muting some resourceelements constituting CSI-RS pattern candidates except for thedetermined CSI-RS pattern, mapping data symbols and CSI-RS to resourceelements in a resource grid with rate patching in consideration of theCSI-RS pattern and muting pattern, and transmitting the data symbols andCSI-RS to a terminal.

In accordance with another aspect of the present invention, a basestation for transmitting CSI-RS and data is provided. The base stationincludes a controller for determining a CSI-RS pattern to be used amongCSI-RS pattern candidates and a muting pattern for muting some resourceelements constituting CSI-RS pattern candidates except the determinedCSI-RS pattern, a resource element mapper for mapping data symbols andCSI-RS to resource elements in a resource grid with rate patching inconsideration of the CSI-RS pattern and muting pattern, and anOrthogonal Frequency Division Multiplexing (OFDM) signal generator formodulating the mapped data symbols and CSI-RS, and an antenna fortransmitting the modulated data symbols and CSI-RS to a terminal.

In accordance with another aspect of the present invention, a method forreceiving, by a terminal, CSI-RS and data is provided. The methodincludes receiving a CSI-RS pattern and a muting pattern transmitted bya base station, receiving a downlink signal from the base station,estimating a channel with the CSI-RS extracted at positions constitutingthe CSI-RS pattern in the received downlink signal, extracting datasymbols from the received downlink signal by referencing the CSI-RSpattern and the muting pattern, and decoding the extracted data symbols.

In accordance with still another aspect of the present invention, aterminal for receiving CSI-RS and data is provided. The terminalincludes an antenna for receiving a downlink signal from a base station,a controller for extracting a CSI-RS pattern and a muting pattern from asignal transmitted by the base station, a channel estimator forestimating a channel with the CSI-RS extracted at positions constitutingthe CSI-RS pattern in the received downlink signal, a symbol extractorfor extracting data symbols from the received downlink signal byreferencing the CSI-RS pattern and the muting pattern, and a decoder fordecoding the extracted data symbols.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description taken in conjunction with theaccompanying drawings, in which.

FIG. 1 is a diagram illustrating a Channel State Information ReferenceSymbol (CSI-RS) reuse pattern and muting pattern according to therelated art;

FIG. 2 is a diagram illustrating configurations of a subframe forsupporting partial muting of a reference signal according to a firstexemplary embodiment of the present invention;

FIG. 3 is a diagram illustrating a characteristic of a partial mutingmethod according to a second exemplary embodiment of the presentinvention;

FIG. 4 is a diagram illustrating configurations of a subframe forsupporting partial muting of a reference signal according to a thirdexemplary embodiment of the present invention;

FIG. 5 is a diagram illustrating configurations of a subframe forsupporting partial muting of a reference signal according to a fourthexemplary embodiment of the present invention;

FIG. 6 is a diagram illustrating a characteristic of a partial mutingmethod according to a fifth exemplary embodiment of the presentinvention;

FIG. 7 is a diagram illustrating a characteristic of a partial mutingmethod according to a sixth exemplary embodiment of the presentinvention;

FIG. 8 is a diagram illustrating a characteristic of a partial mutingmethod according to a seventh exemplary embodiment of the presentinvention;

FIG. 9 is a block diagram illustrating a configuration of a transmittersupporting a muting scheme according to an exemplary embodiment of thepresent invention;

FIG. 10 is a block diagram illustrating a configuration of a receiveraccording to an exemplary embodiment of the present invention;

FIG. 11 is a flowchart illustrating a transmission procedure with amuting scheme according to an exemplary embodiment of the presentinvention; and

FIG. 12 is a flowchart illustrating a reception procedure with a mutingscheme according to an exemplary embodiment of the present invention.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention is provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

Although the description is directed to an Orthogonal Frequency DivisionMultiplexing (OFDM)-based radio communication system, especially abidingby the 3^(rd) Generation Partnership Project (3GPP) Evolved UniversalTerrestrial Radio Access (EUTRA) standard, it should be understood bythose skilled in the art that the present invention can be applied toother communication systems having similar technical background andchannel format, with a slight modification, without departing from thespirit and scope of the present invention.

In the following description, the term “Channel State InformationReference Symbol (CSI-RS) pattern candidate” denotes a CSI-RS reusepattern. The base station can select some of CSI-RS pattern candidatesand some of the rest as muting patterns.

1) Reference Signal Muting Based on Reuse Pattern

As aforementioned, the muting method of the related art mitigates theinterference to the CSI-RSs of other cells by not transmitting signalsin the REs constituting the CSI-RS patterns except for the CSI-RSpattern used by the service cell as shown in part (c) of FIG. 1.However, since the muting method of the related art also has ashortcoming of system throughput reduction, techniques according toexemplary embodiments of the present invention to address the problemare described herein.

FIG. 2 is a diagram illustrating configurations of a subframe forsupporting partial muting of a reference signal according to a firstexemplary embodiment of the present invention.

Referring to FIG. 2, part (a) of FIG. 2 shows an exemplary configurationin which two of 5 CSI-RS patterns, except the CSI-RS pattern of theservice cell, are muted as compared to part (a) of FIG. 1. Unlike themethod of the related art, this method increases the interference to theCSI-RSs of other cells due to no use of muting for all of the reusepatterns, but it is advantageous to secure more REs for datatransmission. In addition to the exemplary case of part (a) of FIG. 2,the muting can be applied with various numbers of patterns and variouscombinations of patterns. By adjusting the number of patterns to applymuting, it is possible to use an optimal muting scheme in view of systemcapacity.

In the first exemplary embodiment, the muting scheme is determinedaccording to the CSI-RS pattern. For example, part (a) of FIG. 2 is themuting scheme in which the resource elements for the CSI-RS patterns 1and 2 in part (a) of FIG. 1 are muted. Part (b) of FIG. 2 is the mutingscheme in which the resource elements for the CSI-RS patterns 3 and 4 inpart (a) of FIG. 1 are muted. Also, part (c) of FIG. 2 is the mutingscheme in which the resource elements for the CSI-RS patterns 3, 4, and5 in part (a) of FIG. 1 are muted.

FIG. 3 is a diagram illustrating a characteristic of a partial mutingmethod according to a second exemplary embodiment of the presentinvention.

The aforementioned muting patterns can be designed using the followingschemes.

In the first muting scheme, the muting pattern is designed as shown inpart (a) of FIG. 3.

In the second muting scheme, two different muting patterns can beapplied at two different times, i.e. time t1 and time t2, as shown inpart (b) of FIG. 3.

In both of the two muting schemes, the muting patterns are determinedthrough negotiation between the transmitter and receiver or notifiedfrom the transmitter to the receiver by a physical layer control signalor a higher layer signal.

In a case where a predetermined muting pattern is used and the mutingpattern is determined according to the cell identifier (cell id), theCSI-RS pattern and muting pattern predefined based on the cell id of thecell to which the receiver performs handover from the current servicecell is applied.

In a case where a predetermined muting pattern is used but it isnecessary to change the muting pattern, the transmitter should notifythe receiver of the change of the muting pattern by means of a physicallayer control signal or a higher layer signal.

In a case where the muting pattern is not predetermined, the transmittershould notify the receiver of the information on the pattern by means ofa physical layer control signal or a higher layer signal.

2) Reference Signal Muting Based on Antenna Port

Unlike the reference signal muting based on the reuse pattern, a schemefor muting the reference signal based on the antenna port is proposedherein.

FIG. 4 is a diagram illustrating configurations of a subframe forsupporting partial muting of a reference signal according to a thirdexemplary embodiment of the present invention.

Referring to FIG. 4, part (a) shows an exemplary configuration in whichthe muting is applied to the signals for the antenna ports 0 and 1, ascompared to the configuration of part (a) of FIG. 1 (using 6 reusepatterns), but not the rest of the antenna ports. The muting can beapplied to the signals for a single antenna port (port 0) as shown inpart (b) of FIG. 4 or less or more antenna ports as compared to the caseof part (a) of FIG. 4. In a special case (i.e., a Long Term EvolutionAdvanced (LTE-A) system), muting the CSI-RS overlapped with aDemodulation Reference Signal (DRS) of Long Term Evolution (LTE) Release8 (antenna port 5) in a position as shown in part (c) of FIG. 4 fallswithin the scope of the present invention.

FIG. 5 is a diagram illustrating configurations of a subframe forsupporting partial muting of a reference signal according to a fourthexemplary embodiment of the present invention.

Referring to FIG. 5, the muting pattern is determined depending on thereuse pattern and antenna port. Part (a) of FIG. 5 shows theconfiguration in which the muting is applied to the reuse patterns 1 and2 and the antenna ports 0 and 1. Part (b) of FIG. 5 shows theconfiguration in which the muting is applied to the reuse patterns 1, 2,and 3 and the antenna ports 6 and 7. As shown in part (c) of FIG. 5, itis possible that the muting is applied to one antenna port for somereuse patterns and multiple antenna ports for other reuse patterns.

Like the reuse pattern-based muting, in the antenna port-based mutingscheme, the muting pattern is determined through negotiation between thetransmitter and receiver or notified from the transmitter to thereceiver by a physical layer control signal or a higher layer signal.

In a case where a predetermined muting pattern is used and the mutingpattern is determined according to the cell id, the CSI-RS pattern andmuting pattern predefined based on the cell id of the cell to which thereceiver performs handover from the current service cell is applied.

In a case where a predetermined muting pattern is used but it isnecessary to change the muting pattern, the transmitter should notifythe receiver of the change of the muting pattern by means of a physicallayer control signal or a higher layer signal.

In a case where the muting pattern is not predetermined, the transmittershould notify the receiver of the information on the pattern by means ofa physical layer control signal or a higher layer signal.

3) Reference Signal Muting Based on Transmission Cycle

This muting scheme defines a muting cycle of a reference signalregardless of the CSI-RS transmission cycle and applies different mutingpatterns according to the muting cycle.

FIG. 6 is a diagram illustrating a characteristic of a partial mutingmethod according to a fifth exemplary embodiment of the presentinvention.

Referring to FIG. 6, a reference signal muting cycle is assigned inaddition to the CSI-RS transmission cycle such that the muting pattern 1and muting pattern 2 can be used alternately according to the mutingsignal. The muting patterns 1 and 2 can be applied to all of the mutingschemes included in the exemplary embodiments of the present inventionas individual muting patterns. The muting scheme can be applied to acase where no muting scheme is used as shown in part (b) of FIG. 1 and acase where all of the reuse patterns are muted as shown in part (c) ofFIG. 1. Although two muting patterns are used in part (a) of FIG. 6,three or more muting patterns can be used alternately as shown in part(b) of FIG. 6. That is, different muting patterns can be appliedaccording to the transmission time point of the subframe (downlinksignal).

In a case of using different muting patterns according to thetransmission time point, the transmission time points and mutingpatterns should be mapped. The mappings between the transmission timepoints and the muting patterns can rotate as the muting pattern changesperiodically. In a case where the muting pattern changes dynamicallyaccording to the channel condition, it is not necessary to fix themapping relationship between the transmission time and muting patternsuch that the muting pattern changes non-periodically.

In a case of changing the muting pattern according to the transmissiontime point, the interferences to the CSI-RS REs of the neighbor cellsare averaged such that it is possible to guarantee the average CSI-RSover a certain level in the neighbor cells.

The change of the muting pattern can be negotiated between thetransmitter and receiver or notified from the transmitter to thereceiver by means of a physical layer control signal or a higher layersignal.

In a case where a predetermined muting pattern is used and the mutingpattern is determined according to the cell id, the CSI-RS pattern andmuting pattern predefined based on the cell id of the cell to which thereceiver performs handover from the current service cell are applied.

In a case where a predetermined muting pattern is used but it isnecessary to change the muting pattern, the transmitter should notifythe receiver of the change of the muting pattern by means of a physicallayer control signal or a higher layer signal.

In a case where the muting pattern is not predetermined, the transmittershould notify the receiver of the information on the pattern by means ofa physical layer control signal or a higher layer signal.

4) Reference Signal Muting Based on Resource Allocation Unit

In this exemplary embodiment, different muting patterns are usedaccording to the frequency band, i.e., the resource allocation unit.Although the description is directed to a case using the PhysicalResource Block (PRB) defined as the frequency resource allocation unitin LTE and LTE-A system in this exemplary embodiment, the resourceallocation unit can be a group of resource blocks aggregated in a systembandwidth (BW) or another type of resource allocation unit in othertypes of systems. That is, the resource allocation unit can include anytype of resource unit defined by aggregation of one or more resources onthe frequency axis.

FIG. 7 is a diagram illustrating a characteristic of a partial mutingmethod according to a sixth exemplary embodiment of the presentinvention.

Referring to FIG. 7, part (a) shows an exemplary case where twodifferent muting patterns are used alternately according to thefrequency resource allocation unit. As shown in part (b) of FIG. 7, itis possible to use three or more different muting patterns alternately.The muting patterns differ from each other and can be applied to all ofthe muting schemes included in the exemplary embodiments of the presentinvention. The muting scheme can be applied to a case where no mutingscheme is used as shown in part (b) of FIG. 1 and a case where all ofthe reuse patterns are muted as shown in part (c) of FIG. 1.

In a case of configuring the muting pattern according to the frequencyband, the interferences to the CSI-RS REs of the neighbor cells areaveraged such that it is possible to guarantee the average CSI-RS over acertain level in the neighbor cells.

The change of the muting pattern can be negotiated between thetransmitter and receiver or notified from the transmitter to thereceiver by means of a physical layer control signal or a higher layersignal.

In a case where a predetermined muting pattern is used and the mutingpattern is determined according to the cell id, the CSI-RS pattern andmuting pattern predefined based on the cell id of the cell to which thereceiver performs handover from the current service cell is applied.

In a case where a predetermined muting pattern is used but it isnecessary to change the muting pattern, the transmitter should notifythe receiver of the change of the muting pattern by means of a physicallayer control signal or a higher layer signal.

In a case where the muting pattern is not predetermined, the transmittershould notify the receiver of the information on the pattern by means ofa physical layer control signal or a higher layer signal.

5) Combined Application of Muting Schemes

In the exemplary embodiments of the present invention, the mutingschemes for determining a muting pattern according to the CSI-RS patternor antenna port are proposed. Also, the muting schemes for determining amuting pattern based on the transmission time point and frequency bandare proposed. These muting pattern determination and application methodscan be combined as far as they are not conflicting with each other.

FIG. 8 is a diagram illustrating a characteristic of a partial mutingmethod according to a seventh exemplary embodiment of the presentinvention.

Referring to FIG. 8, the transmission cycle-based muting scheme is usedin such a way that the reuse pattern-based muting scheme is applied attime t1 and the antenna port-based muting scheme in consideration offrequency band is applied at time t2. Similar to this exemplary case,other combinations of the muting schemes proposed above fall within thescope of the present invention.

6) Block Diagrams and Flowcharts Illustrating Muting Schemes

FIG. 9 is a block diagram illustrating a configuration of a transmittersupporting a muting scheme according to an exemplary embodiment of thepresent invention. The transmitter 900 may be an evolved Node B (eNB)900.

Referring to FIG. 9, the transmit signal is encoded by the transmitter900 into codewords to be transmitted through channel coding and ratematching according to the selected Modulation and Coding Scheme (MCS)level and transmission rank. The scrambling unit 910 performs scramblingon the codewords. The modulation mapper 920 performs modulation on thescrambled codewords at an MCS level. The layer mapper 930 maps themodulation symbols to the corresponding layers 940. The precoding unit950 performs precoding on the modulation symbols mapped to therespective layer 940.

The resource element mapper 970 maps the precoded modulation symbols tothe resource elements. At this time, the control unit 960 determines thepositions carrying the CSI-RS and data and to be muted and controls theresource element mapper 970 to perform resource element mapping based onthe result of the determination. The control unit 960 may also bereferred to as a new CSI-RS mapping and muting controller 960.

The OFDM signal generation unit 980 converts the symbols mapped to theresource elements to OFDM signals. The antenna port 990 transmits theOFDM signals to a receiver.

FIG. 10 is a block diagram illustrating a configuration of a receiveraccording to an exemplary embodiment of the present invention. Thereceiver 1000 may be a User Equipment (UE) 1000.

Referring to FIG. 10, the transmit signal is received through antennaport 1010 of the receiver 1000 via a radio channel. The OFDMdemodulation unit 1020 performs OFDM demodulation on the receivedsignal. The resource decimator 1030 and RS decimator 1050 discriminateamong the CSI-RS and data, and transfers the CSI-RS and data to thechannel estimator 1060 and LLR generator 1070 respectively. At thistime, the controller 1040 locates the positions of CSI-RS, data andmuted positions and informs the resource decimator 1030 and the RSdecimator 1050 of the positions. The controller 1040 may also bereferred to as a new CSI-RS mapping and muting controller 1040. Theresource decimator 1030 and the RS decimator 1050 transfer the valuesacquired at the corresponding REs to the LLR generator 1070 and thechannel estimator 1060. The channel estimator result is transferred tothe LLR generator 1070. The LLR generator 1070 is a component thatextracts a data symbol and thus it is an exemplary implementation of adata symbol extractor. The channel coding decoder 1080 decodes the datasymbol. Finally, the UE can obtain the decoded information 1090.

FIG. 11 is a flowchart illustrating a transmission procedure with amuting scheme according to an exemplary embodiment of the presentinvention.

Referring to FIG. 11, the eNB 900 determines the CSI-RS pattern andmuting pattern to be used in step 1110. As described above, the mutingpattern can be predetermined according to cell id of the eNB 900. Also,there can be a CSI-RS pattern predetermined according to the cell id. Inthis case, it is not necessary for the eNB to inform the UE of themuting pattern. That is, the muting pattern is notified to the UEimplicitly without additional signaling. If no signal is transmitted atan RE, the UE regards the RE as a muted RE. In a case where the eNBnotifies the UE of only whether a muting pattern is used, the UE 1000can determines the muting pattern based on the cell id or otherinformation. The muting pattern also can be determined in considerationwith other elements and, in this case, it is necessary to notify the UE1000 of the muting pattern by signaling explicitly. In the exemplaryembodiment of FIG. 11, the muting pattern is signaled to the UE 1000explicitly.

The eNB 900 signals the CSI-RS pattern and muting pattern to be used tothe UE 1000 by means of a higher layer signal or a physical layercontrol signal in step 1120. Such a signaling is preferably performedwhen the UE 1000 performs handover to enter the coverage of the eNB 900or the eNB 900 changes the CSI-RS pattern or the muting pattern.

For example, the eNB 900 can signal the CSI-RS pattern or muting patternby transmitting a higher layer signal or a physical layer controllercontaining a CSI-RS pattern indicator for indicating the CSI-RS patternto be used and/or a muting pattern indicator for indicating the mutingpattern to be used. Here, the CSI-RS pattern indicator can be a reusepattern identifier. In the exemplary case of part (a) of FIG. 1, theCSI-RS patterns 0 to 5 can be assigned unique CSI-RS pattern indicator,respectively. It is assumed that the information on the mappings betweenthe CSI-RS reuse pattern identifiers and CSI-RS patterns are sharedbetween the eNB 900 and UE 1000.

Also, the muting pattern indicator can be a muting pattern identifier.For example, the identifier 0 can be assigned to the muting pattern ofpart (a) of FIG. 2, the identifier 1 to the muting pattern of part (b)of FIG. 2, the identifier 2 to the muting pattern of part (c) of FIG. 2.It is assumed that the information on the mappings between the mutingpattern identifiers and the muting patterns are shared between the eNB900 and UE 1000.

According to another exemplary embodiment, the muting pattern indicatorcan include at least one of the CSI-RS reuse pattern identifier referredto create a muting pattern and the antenna port identifier. In theexemplary case of part (a) of FIG. 1, the CSI-RS patterns 0 to 5 can beassigned the identifiers 0 to 5, and the antenna port numbers 0 to 7 canbe used as the antenna port identifiers. For example, in a case wherethe muting pattern is generated by referencing the CSI-RS reuse patternidentifier, and if the eNB 900 determines to use the CSI-RS patterns 3and 4 in part (a) of FIG. 1, the identifiers 3 and 4 are transmitted tothe UE 1000 as contained in the muting pattern indicator. Also, in acase of using the antenna port-based muting scheme, if the eNB 900determines to use the muting pattern for the antenna ports 4 and 5 asshown in part (a) of FIG. 1, the identifiers 4 and 5 are transmitted tothe UE 1000 as contained in the muting pattern indicator. In a casewhere the muting pattern is generated by referencing both the CSI-RSreuse pattern identifier and antenna port, if the eNB 900 determines touse the CSI-RS patterns 3 and 4 and antenna ports 4 and 5 in part (a) ofFIG. 1, the CSI-RS reuse pattern identifiers 3 and 4 and the antennaport identifiers 4 and 5 are transmitted to the UE 1000 as combined inthe muting pattern indicator. The muting pattern indicator can beconfigured as shown in Table 1.

TABLE 1 Field CSI-RS pattern identifier field Antenna port identifierfield Data 3, 4 4, 5

Also, the muting pattern indicator can include the information on themapping between the frequency band or the combination of time andfrequency band and the muting pattern.

For example, if the transmission time is t, it is assumed that themuting pattern 0 is selected for the case where the remainder obtainedby dividing the t by 4 is 0 or 1, the muting pattern 1 is selected forthe case where the remainder is 2, and the muting pattern 2 is selectedfor the case where the remainder is 3. In this case, the information onthe mapping of the muting pattern to the time point is transmitted tothe UE 1000 as contained in the muting pattern indicator. Table 2 showsexemplary mappings between the muting patterns and time points.

TABLE 2 T mod 4 0 1 2 3 Muting pattern identifier 0 0 1 2

In a case where the muting pattern is determined according to thefrequency band, the information on the mappings between the mutingpatterns and frequency bands is transmitted to the UE 1000 as containedin the muting pattern indicator. Table 3 shows exemplary mappingsbetween the muting patterns and frequency band.

TABLE 3 Frequency band identifier 0 1 2 3 Muting pattern identifier 0 11 2

The frequency band identified by the identifier 0 is assigned the mutingpattern 0.

The frequency band identified by the identifier 1 is assigned the mutingpattern 1.

The frequency band identified by the identifier 2 is assigned the mutingpattern 2.

In a case where the muting pattern is determined according to thecombination of the transmission time point and frequency band, theinformation on the mappings between the muting patterns and thecombinations of the transmission time points and frequency bands aretransmitted to the UE 1000 as contained in the muting pattern indicator.Table 4 shows exemplary mappings between the muting patterns and thecombinations of the transmission time points and frequency bands.

TABLE 4 Frequency Frequency Frequency Frequency Band 0 band 1 band 2Band 3 T mod 4 = 0 Muting pattern 0 Muting pattern 1 Muting pattern 1Muting pattern 2 T mod 4 = 1 Muting pattern 0 Muting pattern 0 Mutingpattern 0 Muting pattern 0 T mod 4 = 2 Muting pattern 0 Muting pattern 3Muting pattern 0 Muting pattern 0 T mod 4 = 3 Muting pattern 0 Mutingpattern 4 Muting pattern 0 Muting pattern 0

The frequency band 0 is assigned the muting pattern 0 regardless oftransmission time point. The frequency band 1 is assigned a series ofmuting patterns 1, 0, 3 and 4 as cyclically time progresses.

Although the mapping information itself can be transmitted in the mutingpattern indicator as shown in tables 2 to 4, it is also possible totransmit the identifiers of the mapping information as contained in themuting pattern indicator.

A description is made of another exemplary embodiment of a muting schemesignaling from the transmitter (eNB) 900 to the receiver (UE) 1000.

In the signaling method described hereinafter, the signal can betransmitted by means of a physical layer control signal or a higherlayer signal or in other methods. The system supporting the mutingsystems can include some or entire features of the signaling method thatare described hereinafter.

(a) The transmitter (eNB) transmits a 1-bit muting on/off signal to thereceiver (UE).

(b) The UE can be aware of the muting pattern according to the cell idof the serving cell or frame number, OFDM symbol position (index) atwhich the CSI-RS is transmitted in the subframe, CSI-RS transmissioncycle, muting cycle, number of cells that belong to a CoordinatedMultiPoint (CoMP) set, entire system bandwidth, and size of a sub-band.

(c) The transmitter (eNB) transmits an N-bit signal informing of themuting to the receiver (UE). The N-bit signal can be interpreted into 2Nstates for indicating one of the muting patterns predetermined accordingto the cell id of the serving cell or frame number, OFDM symbol position(index) at which the CSI-RS is transmitted in the subframe, CSI-RStransmission cycle, muting cycle, number of cells that belong to theCoMP set, entire system bandwidth, and size of a sub-band; and thenumber of interpreted states can be larger than 2N. Here, the 2N statescan include a state for indicating no muting.

(d) In a case of reuse pattern-based muting scheme, it is possible toinform of the reuse pattern to be muted using the same method describedat item (c) or only the position of the antenna port 0 of the reusepattern to be muted. In a case of information of the antenna port 0, theUE can be aware of the positions of REs to be muted that correspond tothe rest of the antenna ports based on the position of the antenna port0 without additional signaling. The positions of the rest of the REs tobe muted can be determined differently according to the cell id of theserving cell or frame number, OFDM symbol position (index) at which theCSI-RS is transmitted in the subframe, CSI-RS transmission cycle, mutingcycle, number of cells that belong to the CoMP set, entire systembandwidth, and size of a sub-band.

(e) In a case of antenna port-based muting scheme, the N-bit signal canbe used to notify of the 2N antenna ports to be muted. At this time, theport number of the antenna port to be muted can be determineddifferently according to the cell id of the serving cell or framenumber, OFDM symbol position (index) at which the CSI-RS is transmittedin the subframe, CSI-RS transmission cycle, muting cycle, number ofcells that belong to the CoMP set, entire system bandwidth, and size ofa sub-band.

(f) The transmitter (eNB) can determine the muting cycle and notify thereceiver (UE) of the muting cycle. In a case where the muting cycle isnot informed, the UE can use the muting cycle negotiated in advancebetween the transmitter and the receiver or apply muting always in thesubframes carrying CSI-RS. Although the CSI-RS transmission cycle andthe muting cycle are identical with each other, the CSI-RS transmissionand muting may not occur in the same subframe. The signal for notifyingof the muting cycle can be interpreted differently according to the cellid of the serving cell or frame number, OFDM symbol position (index) atwhich the CSI-RS is transmitted in the subframe, CSI-RS transmissioncycle, muting cycle, number of cells that belong to the CoMP set, entiresystem bandwidth, and size of a sub-band.

(g) In the frequency resource-based muting, different patterns can beapplied for individual UEs. In view of the frequency axis, differentmuting patterns can be applied in a unit of one or more Resource Blocks(RBs) or Resource Block Groups (RBGs), or a sub-band for feedback, orother frequency axis resource unit. The muting patterns also include thenon-muting pattern. The frequency axis resource unit can be determineddifferently according to the cell id of the serving cell or framenumber, OFDM symbol position (index) at which the CSI-RS is transmittedin the subframe, CSI-RS transmission cycle, muting cycle, number ofcells that belong to the CoMP set, entire system bandwidth, and size ofa sub-band.

The eNB 900 calculates a number of data symbols to be transmitted andperforms rate matching of data to be transmitted based on the number ofdata symbols in consideration of the CSI-RS pattern and muting patternto be used in step 1130. Next, the eNB 900 maps the data symbols toempty REs in consideration of CSI-RS, DeModulation Reference Signal(DM-RS), Rel-8 DRS, and muting positions in step 1140. Next, the eNB 900maps the CSI-RS, DM-RS, and Rel-8 DRS to corresponding positions in step1150. Finally, the eNB 900 transmits the downlink signal of the datasymbols and RSs after performing OFDM modulation thereon in step 1160.

FIG. 12 is a flowchart illustrating a reception procedure with a mutingscheme according to an exemplary embodiment of the present invention.

The embodiment of FIG. 12 shows a procedure in which the receiver 1000receives a muting pattern signaling. If no muting pattern is signaled,the UE 1000 executes the procedure in a similar manner regardless of amuting pattern.

Referring to FIG. 12, the UE 1000 receives a physical layer controlsignal or higher layer signal transmitted by the transmitter (eNB) 900in step 1210. The UE 1000 checks the CSI-RS, DM-RS, and muting positionsbased on the received physical channel control signal or higher layersignal in step 1220. At this time, the positions of the CSI-RS andmuting can be determined by interpreting the received control signal andhigher layer signal according to a predetermined method. The UE 1000receives the OFDM symbols (subframe) in step 1230. Afterward, steps1240, 1270, and 1280 can be executed individually in parallel. Steps1240, 1270 and 1280 can be executed simultaneously or in a certainorder.

The UE 1000 extracts the CSI-RS from the received OFDM symbols(subframe) in step 1240 and checks the positions of the CSI-RS, DM-RS,and data symbols and executes channel estimation based on the CSI-RSextracted. The UE 1000 generates feedback information of CQI, PMI, andRI based on the channel estimation in step 1250 and feeds back the CQI,PMI, and RI to the eNB in step 1260.

As an additional process, the UE 1000 extracts DM-RSs from the receivedOFDM symbols in step 1270. The UE 1000 executes channel estimation basedon the extracted DM-RS. The UE 1000 receives data symbols at the REs ina Physical Downlink Shared Channel (PDSCH) region except for thepositions of REs to which the CSI-RS, DM-RS, and Rel-8 DRS, and muted instep 1280. The UE 1000 performs data symbol demodulation with thechannel estimation value acquired based on the DM-RSs in step 1290.

As described above, the method and apparatus for transmitting CSI-RS anddata according to exemplary embodiments of the present invention iscapable of improving channel estimation performance, thereby addressingthe system throughput degradation problem of the muting method of therelated art and may improve entire system capacity.

It will be understood that each block of the flowchart illustrationsand/or block diagrams, and combinations of blocks in the flowchartillustrations and/or block diagrams, can be implemented by computerprogram instructions. These computer program instructions may beprovided to a processor of a general purpose computer, special purposecomputer, or other programmable data processing apparatus to produce amachine, such that the instructions, which execute via the processor ofthe computer or other programmable data processing apparatus, createmeans for implementing the functions/acts specified in the flowchartand/or block diagram block or blocks. These computer programinstructions may also be stored in a computer-readable memory that candirect a computer or other programmable data processing apparatus tofunction in a particular manner, such that the instructions stored inthe computer-readable memory produce an article of manufacture includinginstruction means which implement the function/act specified in theflowchart and/or block diagram block or blocks. The computer programinstructions may also be loaded onto a computer or other programmabledata processing apparatus to cause a series of operational steps to beperformed on the computer or other programmable apparatus to produce acomputer implemented process such that the instructions which execute onthe computer or other programmable apparatus provide steps forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

Furthermore, the respective block diagrams may illustrate parts ofmodules, segments or codes including at least one or more executableinstructions for performing specific logic function(s). Moreover, itshould be noted that the functions of the blocks may be performed indifferent order in several modifications. For example, two successiveblocks may be performed substantially at the same time, or may beperformed in reverse order according to their functions.

The term “module” according to the embodiments of the invention, means,but is not limited to, a software or hardware component, such as a FieldProgrammable Gate Array (FPGA) or Application Specific IntegratedCircuit (ASIC), which performs certain tasks. A module mayadvantageously be configured to reside on the addressable storage mediumand configured to be executed on one or more processors. Thus, a modulemay include, by way of example, components, such as software components,object-oriented software components, class components and taskcomponents, processes, functions, attributes, procedures, subroutines,segments of program code, drivers, firmware, microcode, circuitry, data,databases, data structures, tables, arrays, and variables. Thefunctionality provided for in the components and modules may be combinedinto fewer components and modules or further separated into additionalcomponents and modules. In addition, the components and modules may beimplemented such that they execute one or more Central Processing Units(CPUs) in a device or a secure multimedia card.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for transmitting a channel stateinformation reference signal (CSI-RS) by a base station, the methodcomprising: selecting a CSI-RS pattern including a first set of resourceelements (REs); selecting a muting pattern including a second set ofREs; transmitting an indicator indicating the muting pattern among aplurality of predefined muting patterns and period information appliedto the muting pattern via higher layer signaling; mapping data symbolsand the CSI-RS to REs based on the CSI-RS pattern and the mutingpattern; and transmitting the data symbols and the CSI-RS to a userequipment (UE), wherein the data symbols are mapped to REs that are notincluded in the CSI-RS pattern and the muting pattern, wherein themuting pattern is selected among the plurality of predefined mutingpatterns and the plurality of predefined muting patterns are included ina set of CSI-RS pattern candidates, and wherein the indicator comprisesa plurality of bits corresponding to the plurality of predefined mutingpatterns.
 2. The method of claim 1, wherein the first set of REs and thesecond set of REs are composed of a pair of REs.
 3. The method of claim1, wherein the CSI-RS pattern and the muting pattern are included in theset of CSI-RS pattern candidates.
 4. A method for receiving a channelstate information reference signal (CSI-RS) by a user equipment (UE),the method comprising: receiving an indicator indicating a mutingpattern among a plurality of predefined muting patterns and periodinformation applied to the muting pattern via higher layer signaling;receiving data symbols and the CSI-RS mapped to resource elements (REs)from a base station; extracting the data symbols based on a CSI-RSpattern including a first set of REs and the muting pattern including asecond set of REs; wherein the data symbols are mapped to REs that arenot included in the CSI-RS pattern and the muting pattern, wherein themuting pattern is selected among the plurality of predefined mutingpatterns and the plurality of predefined muting patterns are included ina set of CSI-RS pattern candidates, and wherein the indicator comprisesa plurality of bits corresponding to the plurality of predefined mutingpatterns.
 5. The method of claim 4, wherein the first set of REs and thesecond set of REs are composed of a pair of REs.
 6. The method of claim5, wherein the CSI-RS pattern and the muting pattern are included in theset of CSI-RS pattern candidates.
 7. A base station for transmitting achannel state information reference signal (CSI-RS), the base stationcomprising: a transceiver transmitting and receiving signals to and froma user equipment (UE); and a controller controls to select a CSI-RSpattern including a first set of resource elements (REs), select amuting pattern including a second set of REs, to transmit an indicatorindicating the muting pattern among a plurality of predefined mutingpatterns and period information applied to the muting pattern via higherlayer signaling, map data symbols and the CSI-RS to REs based on theCSI-RS pattern and the muting pattern, and transmit the data symbols andthe CSI-RS to a user equipment (UE), and wherein the data symbols aremapped to REs that are not included in the CSI-RS pattern and the mutingpattern, wherein the muting pattern is selected among the plurality ofpredefined muting patterns and the plurality of predefined mutingpatterns are included in a set of CSI-RS pattern candidates, and whereinthe indicator comprises a plurality of bits corresponding to theplurality of predefined muting patterns.
 8. The base station of claim 7,wherein the first set of REs and the second set of REs are composed of apair of REs.
 9. The base station of claim 7, wherein the CSI-RS patternand the muting pattern are included in the set of CSI-RS patterncandidates.
 10. A user equipment apparatus for receiving a channel stateinformation reference signal (CSI-RS), the apparatus comprising: atransceiver transmitting and receiving signals to and from a basestation; and a controller controls to receive an indicator indicating amuting pattern among a plurality of predefined muting patterns andperiod information applied to the muting pattern via higher layersignaling, to receive data symbols and the CSI-RS mapped to resourceelements (REs) from a base station, and extract the data symbols basedon a CSI-RS pattern including a first set of REs and the muting patternincluding a second set of REs, and wherein the data symbols are mappedto REs that are not included in the CSI-RS pattern and the mutingpattern, wherein the muting pattern is selected among the plurality ofpredefined muting patterns and the plurality of predefined mutingpatterns are included in a set of CSI-RS pattern candidates, and whereinthe indicator comprises a plurality of bits corresponding to theplurality of predefined muting patterns.
 11. The apparatus of claim 10,wherein the first set of REs and the second set of REs are composed of apair of REs.
 12. The apparatus of claim 10, wherein the CSI-RS patternand the muting pattern are included in the set of CSI-RS patterncandidates.